It is known to add hydrazine compounds to silver halide photographic emulsions or developing solutions. For example, the addition of hydrazine compounds to silver halide photographic emulsions or developing solutions is disclosed in U.S. Pat. No. 3,730,727 (developing solution containing a combination of ascorbic acid and hydrazine), U.S. Pat. No. 3,227,552 (the use of hydrazine as an auxiliary developing agent to obtain direct positive color image), U.S. Pat. No. 3,386,831 (silver halide light-sensitive material containing .beta.-monophenylhydrazide of an aliphatic carboxylic acid as a stabilizer), U.S. Pat. No. 2,419,975 and Mees, The Theory of Photographic Process, the third edition, (1966), page 281.
In particular, U.S. Pat. No. 2,419,975 discloses a method for obtaining high contrast negative image by adding hydrazine compounds.
In the specification of that patent, it is disclosed that extremely high-contrast photographic characteristics having a gamma (.gamma.) value exceeding 10 can be obtained when hydrazine compounds are added to silver chlorobromide emulsions, and when photographic materials are processed with developing solutions having a pH of as high as 12.8. However, strongly alkaline developing solutions having a pH near 13 are liable to be oxidized by air. They are therefore unstable and can not be stored or used over a long period of time.
Superhigh-contrast photographic characteristics having a gamma value exceeding 10 are useful for the reproduction of line drawing and for the photographic reproduction of continuous image by dot image useful for printing plate making in the case of both negative and positive images.
To achieve this object, there have been conventionally used methods wherein photographic emulsions comprising silver chlorobromide having a silver chloride content of higher than 50 mol %, preferably 75 mol % are used and development is carried out with hydroquinone developing solutions containing sulfite ion at an extremely low effective concentration (generally not higher than 0.1 mol/l). However, the low concentration of sulfite ion in the developing solutions results in the developing solutions being very unstable and being preserved for only 3 days at the most. Further, silver chlorobromide emulsions having a relatively high silver chloride content must be used and hence high sensitivity cannot be obtained. Accordingly, there has been a demand to obtain superhigh-contrast photographic characteristics useful for the reproduction of dot image or line drawing by using high-sensitivity emulsions and stable developing solutions.
U.S. Pat. Nos. 4,224,401, 4,168,977, 4,243,739, 4,272,614 and 4,323,643 disclose silver halide photographic emulsions which give extremely high-contrast negative photographic characteristics with stable developing solutions. However, it has been found that the acyl hydrazine compounds used therein have certain disadvantages.
Namely, it is known that these hydrazine compounds evolve nitrogen gas during development. The gas is accumulated in the film to form bubbles which damage the photographic image. Further, the gas flows into the developing solutions so that other photographic materials are adversely affected.
It is known that increasing the molecular weights of nucleating agents, to thereby make the agents nondiffusing, is a means for preventing gas from flowing into the developing solutions. However, it has been found that conventional nucleating agents which were made nondiffusing in this manner, reduce the stability of emulsions over time. Namely, when coating solutions containing those nucleating agents are left to stand, precipitates are formed in the coating solutions, filterability deteriorates and further photographic performance causes change.
Furthermore, these conventional hydrazine compounds must be used in large quantities for the purposes of sensitization and imparting high contrast. They also generally cause sensitization and an increase in fogging with time during storage when high-sensitivity photographic materials in particular are required and when the hydrazine compounds are used in combination with other sensitizing techniques (e.g., an increase in chemical sensitization; an increase in grain size; and the addition of compounds which accelerate sensitization as described in U.S. Pat. Nos. 4,272,606 and 4,241,164).
Accordingly, there has been a demand for compounds which reduce the evolution of bubbles or the outflow of gas into the developing solutions do not have a problem with respect to stability with time, and give extremely high contrast photographic characteristics by the use of a very small amount thereof.
U.S. Pat. Nos. 4,385,108, 4,269,929 and 4,243,739 disclose that extremely high contrast negative gradation photographic characteristics can be obtained by using hydrazine compounds having substituents which can be easily adsorbed by silver halide grains.
Among these hydrazine compounds having adsorptive groups, those exemplified in the above patent specifications have the disadvantage that they cause desensitization with time during storage. Hence, it is necessary to choose compounds which do not cause the above-described problem.
On the other hand, many direct positive photographic processes are known. Among them, the most useful are (1) a process wherein silver halide grains previously fogged are exposed in the presence of a desensitizer and then development is carried out and (2) a process wherein silver halide emulsions having sensitivity speck predominantly in the interior of silver halide grains are exposed and then development is carried out in the presence of a nucleating agent. The present invention relates to the latter process. A silver halide emulsion in which sensitivity speck exists predominantly in the interiors of silver halide grains and a latent image is predominantly formed in the interiors of the grains, is called an internal latent image type silver halide emulsion which can be distinguished from silver halide grains in which a latent image is predominantly formed on the surfaces of the grains.
There are known methods for obtaining direct positive image by subjecting the internal latent image type silver halide emulsion to surface development in the presence of a nucleating agent and photographic emulsions and photographic materials used for said methods, as disclosed in Research Disclosure, No. 23510 (November, 1983).
In the above methods for obtaining a direct positive image, nucleating agents may be added to developing solutions, but good reversal characteristics can be obtained when the nucleating agents are adsorbed on the surfaces of silver halide grains by adding the agents to the photographic emulsion layers of the photographic material or to the other appropriate layers thereof.
Examples of nucleating agents used in the above processes for obtaining a direct positive image are hydrazine compounds described in U.S. Pat. Nos. 2,563,785 and 2,588,982; hydrazide and hydrazine compounds described in U.S. Pat. No. 3,227,552; heterocyclic quaternary salt compounds described in U.S. Pat. Nos. 3,615,615, 3,719,494, 3,734,738, 4,094,683 and 4,115,122, British Patent 1,283,835, JP-A-52-3426 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") and JP-A-52-69613; thio urea linking type acylphenyl hydrazine compounds described in U.S. Pat. Nos. 4,030,925, 4,031,127, 4,139,387, 4,245,037, 4,255,511 and 4,276,364 and British Patent 2,012,443; compounds having a heterocyclic thioamido group on the adsorption group described in U.S. Pat. No. 4,080,207; phenylacylhydrazine compounds having mercapto group-containing heterocyclic groups as the adsorption group described in British Patent 2,011,397B; sensitizing dyes having a substituent having a nucleating effect in the molecular structure described in U.S. Pat. No. 3,718,470; and hydrazine compounds described in JP-A-59-200230, JP-A-59-212828, JP-A-59-212829 and Research Disclosure, No. 23510 (November, 1983).
However, it has been found that all of these compounds have disadvantages. For example, some compounds are low in activity as a nucleating agent; those having high activity are poor in preservability; some compounds cause a change in activity between the time that the compound is added to the emulsion and the time that the emulsion is coated onto a support; and the quality of the layers deteriorates when large amounts of the compounds are added.
With the purpose of solving these problems, there have been proposed adsorption-type hydrazine derivatives described in JP-A-60-l79734, JP-A-61-170733, JP-A-62-65034, JP-A-62-948, and JP-A-61-270744, hydrazine derivatives having a heterocyclic aromatic ring in the molecular structure described in JP-A-62-275247; and hydrazine derivatives having a modifying group described in JP-A-62-270948 and JP-A-63-29751. However, all of these compounds have disadvantages. For example, the nucleating activity is insufficient for the requirement of lowering the pH of processing solutions to increase the stability of developing solutions (namely to prevent developing agents from being deteriorated), and for the requirement of shortening the processing time of development to reduce dependence on variation of the composition of the developing solutions (e.g., pH, sodium sulfite). Or they cause an adverse effect by the outflow thereof into the developing solutions.